Break In Disaster????????

Do you have the right washers on the rocker shaft hold down bolts? They should like this one, and are formed around the shaft. The 2nd and 4th washers are wider than the 1st, 3rd, and 5th. Perhaps the bolt or washer is not down right.

Did you perchance use cam bearings with full grooves? That will put a much higher level of pressure into the rocker shaft than normal.